1. Field of the Invention
The present invention relates to a dielectric ceramic composition and a ceramic electronic part using the same. More particularly, the present invention relates to a dielectric ceramic composition suitable as a dielectric material of a ceramic electronic part for use in a high frequency region and to a ceramic electronic part using the dielectric ceramic composition.
2. Description of the Related Art
Ceramic electronic parts such as ceramic capacitors, filters, resonators and so on are provided with a dielectric layer which is formed by a firing step. The firing in the firing step is usually carried out at a high temperature over 1,000.degree. C. or higher. A filter medium for a firing oven, a sagger or a setter may be worn off and a firing oven may entail the high cost of electricity for heating the firing oven at a high temperature. As a consequence, the cost of manufacturing ceramic electronic parts may become expensive. Therefore, a variety of techniques have hitherto been proposed to provide processes for preparing dielectric ceramic compositions which can sustain various electrical features at desired levels even if they have been firing at a relatively low temperature.
For instance, Japanese Patent Unexamined Publication No. 4-359,806 discloses a dielectric ceramic composition having a composition of component systems consisting of a BaTiO.sub.3 -Nd.sub.2 O.sub.3 -Sm.sub.2 O.sub.3 -TiO.sub.2 system, Al.sub.2 O.sub.3, and a SiO.sub.2 -PbO-CaO-B.sub.2 O.sub.3 -Na.sub.2 O-MgO-K.sub.2 O system and having a limited rate of an amount of each component.
The dielectric ceramic composition disclosed in the prior publication can be fired at a temperature as low as 1,000.degree. C. or lower and it can sustain its remarkable features that a Q factor and a specific resistance are high at the dielectric constant of 10 or higher even under firing conditions under a partial oxygen pressure low enough to cause no oxidation of copper and that a rate of a variation in an electrostatic capacity with temperature is very small. Further, the composition disclosed therein can provide a dielectric filter highly suitable for a high frequency at low manufacturing costs and with improved durability because it uses a base metal such as copper or the like as a conductive material. Moreover, the prior art technology can realize a process for the preparation of such a dielectric filter.
Further, for instance, Japanese Patent Unexamined Publication No. 4-359,810 discloses a dielectric ceramic composition having a composition of component systems consisting of Al.sub.2 O.sub.3, a SiO.sub.2 -PbO-CaO-B.sub.2 O.sub.3 -Na.sub.2 O-MgO-K.sub.2 O system, and a BaO-TiO.sub.2 system or a BaO-Nb.sub.2 O.sub.3 -TiO.sub.2 system or a BaO-Sm.sub.2 O.sub.3 -TiO.sub.2 system and having a limited rate of an amount of each component.
Likewise, the dielectric ceramic composition disclosed in the prior publication can be fired at a temperature as low as 1,000.degree. C. or lower and it can sustain its remarkable features that a Q factor and a specific resistance are high at the dielectric constant of 10 or higher even under firing conditions at a partial oxygen pressure low enough to cause no oxidation of copper and that a rate of a variation in an electrostatic capacity with temperature is very small. Further, the composition disclosed therein can provide a dielectric filter highly suitable for a high frequency at low manufacturing costs and with improved durability because it uses a base metal such as copper or the like as a conductive material. Moreover, it can realize a process for the preparation of such a dielectric filter.
Firing those prior art dielectric ceramic compositions at the temperature as low as 1,000.degree. C. or lower, however, cannot be said to be sufficiently low in terms of the firing temperature in order to be applied to ceramic electronic parts because the upper limit of the firing temperature should be approximately 920.degree. C. as long as the use of a metallic material having a low melting point, such as Ag or the like, or a base metal material is used as a material for an inner electrode, etc. is taken into account.